Vacuum cleaners have previously been proposed wherein there was an automatic height adjustment of the nozzle relative to the floor, such as shown in U.S. Letters Pat. Nos. 2,555,887; 2,583,054; 2,592,710: and 4,706,327. These were usually sufficiently complicated mechanisms that they were not commercially successful.
Vacuum cleaners have also been proposed utilizing a diaphragm to sense the amount of vacuum either to vary a resistance, as in U.S. Pat. No. 4,021,879, to slow the electric motor, or to actuate indicator lamps as disclosed in U.S. Pat. Nos. 4,199,838 and 4,481,692.
Other vacuum cleaners have been proposed which utilize some form of sensor to indicate when the filter bag is full and requires changing as in U.S. Pat. Nos. 4,199,838 and 4,342,133. Still other patents have had some form of indication of brush speed, either by a Hall effect sensor, as in U.S. Pat. No. 4,245,370, or by a magnet and sensor coil, as in U.S. Pat. Nos. 4,692,754 and 4,728,942.